Construction estimator
TMT Steel Weight Calculator
Pick the bar diameter, enter the length of each bar and how many you have to get the weight in kilograms and tonnes. Your entered values stay out of analytics.
Formula and assumptions
Weight per metre = π ÷ 4 × diameter² × 7,850 kg/m³, with the diameter in metres. Weight per bar = weight per metre × length. Total weight = weight per metre × length × number of bars × (1 + wastage).
- Plain round bars of the nominal diameter, with a steel density of 7,850 kg/m³.
- Weight per metre = π ÷ 4 × diameter² × density. The shortcut diameter² ÷ 162 is about 0.1% to 0.2% higher; this tool uses the exact formula.
- Wastage, if you enter any, is added to the total length. It is 0% by default, so the result is the physical weight.
- Weight only. It does not cover bar-bending schedules, laps, hooks, steel grades or structural design.
- Weight per metre is shown to 3 decimal places, kilograms to 2 and tonnes to 3 (half up). Nothing is rounded up to bundles or whole bars.
Formula version 1.0, last reviewed Reviewed by an external trade reviewer, 6 October 2026; released by the owner.
Frequently asked questions
Why not use diameter squared divided by 162?
That shortcut is close but about 0.1% to 0.2% high at most sizes. This calculator uses the exact formula, which is the calculation behind the usual weight-per-metre tables.
What density is used?
7,850 kg per cubic metre, the usual figure for steel.
Is my bar's weight exactly this?
Actual bar mass may vary within the applicable manufacturing tolerance, so a weighbridge figure can differ slightly from the calculated weight. The calculation gives the theoretical nominal weight, not the weight of a delivered bar.
Does it include laps, hooks and bends?
No. It weighs the total length you enter. Add the extra length for laps and bends yourself, or use the optional wastage allowance.
What does this not include?
Bar-bending schedules, development lengths, steel grades and strengths, and any structural design. It reports weight only.